Steel-shelled ceramic spacer block

ABSTRACT

A spacer member for supporting a metallic alloy product during heat treatment comprising a ceramic core and a tubular housing is disclosed. The tubular housing, which encloses the ceramic core, comprises a bore, a wall portion, and two end portions. In order to resist deformation during usage, the tubular housing is made from high temperature steel, a high temperature steel alloy, or cold rolled steel. The wall portion has at least two substantially flat surfaces having corner edges that have a radius of at least ⅜ inch and ends that are tapered at least ¼ inch. In addition, the flat surfaces also have a coating that reduces the sticking of a metallic alloy product. The end portions each have at least one aperture to allow the inside to adjust itself to ambient atmospheric pressure. A method of making a spacer member is also disclosed.

FIELD OF THE INVENTION

The present invention relates to spacer blocks positioned betweenaluminum ingots in preheat furnaces and, more particularly, to animproved spacer block that is more robust and has a longer useful life.

BACKGROUND OF THE INVENTION

Heating of aluminum ingots is a well-established practice for achievingdesired properties in the ingot and to render the ingot sufficientlymalleable for reduction in thermo-mechanical processes. During apreheating step, aluminum ingots are heated to temperatures below themelting point of the aluminum alloy. Preheating serves to control themetallurgical properties of the ingot, reduce cracking, and reduce theforces needed to further process the ingot. Up to six ingots cantypically be vertically stacked in a preheat furnace at one time. Spacerblocks are typically positioned between the stacked ingots to maintain agap between the ingots and prevent them from sticking to one another,allow hot gases to circulate between the ingots for faster heat-up, andprovide uniform exposure to the furnace atmosphere.

Conventional blocks are solid blocks of an aluminum alloy, which may bethe same as or different from the alloy of the ingot supported therebyand have a size of about 1 to 4 inches×2 to 6 inches×6 to 24 inches.Each of these spacer blocks weighs over ten pounds. A single operatormay handle 400 to 500 spacer blocks per shift.

Additional drawbacks to conventional spacer blocks relate to theircomposition. When heated in a furnace, the metal of the ingot as well asthe metal of the spacer blocks soften. When aluminum alloy spacer blocksare subjected to the weight of a conventional ingot load in a preheatfurnace and temperatures of about 600° F. (316° C.) and higher, thestrength of the spacer block begins to decrease. When subjected tohigher preheat furnace temperature conditions of about 800° F. (427° C.)and higher, aluminum alloy spacer blocks exhibit a diminished strengthcapacity that is typically unsatisfactory for providing adequate ingotsupport.

In addition, oxide layers grow and volatile metals, such as magnesiumand lithium, migrate to the surfaces of the spacer blocks and theingots. The migrated metals cause the spacer blocks and the ingots toadhere to one another. Deformation and adhesion of the spacer blocks tothe ingots is particularly problematic for the ingots at the bottom ofthe stack where the load is the greatest. When the preheat cycle iscomplete, a crane is used to remove an ingot from the stack and positionthe ingot at the beginning of a hot line rolling mill, reversing mill,or the like. An operator must remove any spacer blocks stuck to theingot prior to any ingot processing. Occasionally, the spacer block canbe removed from the ingot by simple hand pressure. However, often thespacer block is so tightly adhered to the ingot that it must be knockedoff with a large hammer or an axe. Occasionally, a forklift or the likemust be used to loosen the adhered spacer block from the surface of theingot.

An additional problem associated with sticking of conventional spacerblocks to the ingot is the formation of marks, which are typically lefton an ingot upon removal of the spacer block. Spacer blocks oftenproduce defects in the surface of the ingot. When an ingot having such adefect is subsequently rolled, the defect becomes a surface imperfectionin the rolled product. For many applications of rolled product, suchdefects are unacceptable in the marketplace.

Another drawback to the aluminum spacer blocks is the tendency ofvarious aluminum alloys used for conventional spacer blocks to creep athigh temperatures. At temperatures of about 900-1140° F. (482-616° C.),conventional spacer blocks having initial dimensions of 3 inch×3 inch'12inch can become deformed into dimensions of about 2.5 inch×3.5 inch×12.5inch. Not all spacer blocks in a stack of ingots are always deformedsimilarly. Hence, in a set of spacer blocks used with a stack of ingots,the individual spacer blocks may have differing dimensions. Variabledimensions in the spacer blocks can aggravate sticking of the spacerblocks to the ingots. For example, when six spacer blocks are used foran ingot and two of the spacer blocks do not touch the ingot becausethey have been deformed, only four of the spacer blocks contact theingot, thereby supporting the entire load. In this situation, the loadper unit area borne by the four spacer blocks contacting the ingotincreases by about 33%. At such higher loads, the adhesion between thespacer blocks and the ingots is aggravated.

High temperature creep of aluminum spacer blocks is also a problem inpreheat furnaces operated at higher temperatures, e.g., at or aboveabout 1120° F. (604° C.). It has become common practice in thosecircumstances to position the spacer blocks between the ingots so that aportion of the spacer block extends out between the ingots. During thepreheat cycle, the portion of the spacer block which is sandwichedbetween the ingots becomes flattened to a thickness of about ½ inchwhile the remaining portion of the spacer block which did not supportthe ingot retains its original width and height of 3 inch×3 inch. Inorder to reuse spacer blocks that have been partially flattened,operators turn the spacer blocks between ingots. This often results inthe entire spacer block being flattened into a thickness of about ½.When the spacer block between the ingots is greatly reduced to about ½inch, airflow between the ingots is greatly reduced which results inuneven heating, extended cycle times, and insufficient exposure of theingot surfaces to the furnace atmosphere.

Accordingly, a need exists for a spacer block for use in aluminum ingotpreheat furnaces which is lightweight, does not stick to the ingotsurfaces, and retains its shape when subjected to high temperaturefurnace conditions.

SUMMARY OF THE INVENTION

This need is met by the spacer member of the present invention, whichmay be used for supporting a metallic alloy product subject to heattreatment. The spacer block comprises a tubular housing with a core of aceramic material. The tubular housing, which encloses the ceramic core,comprises a wall portion, two end portions, and a bore. The wall portionhas at least two substantially flat surfaces in parallel with eachother, with the flat surfaces having corner edges that have a radius ofat least 3/8 inch and ends that are tapered at least ¼ inch inwardtoward the bore of the tubular housing. In addition, the flat surfacesalso have a coating that reduces the sticking of a metallic alloyproduct. The end portions each have at least one aperture to allow theinternal portions of the block to adjust to ambient atmosphericpressure.

The spacer member of the present invention may be produced by providinga tubular housing comprising a bore and a wall portion having at leasttwo substantially flat surfaces in parallel with each other wherein theflat surfaces have corner edges and ends, tapering the ends at least ¼inch inward toward the bore of the tubular housing, attaching an endportion having at least one aperture to an end of the tubular housing,filling the tubular housing with a ceramic material, and attachinganother end portion having at least one aperture to the other end of thetubular housing. The flat surfaces may then be coated with a non-stickcoating for preventing sticking of a heat-treated metallic alloy productto the spacer member.

A complete understanding of the invention will be obtained from thefollowing description when taken in connection with the accompanyingdrawing figures wherein like reference characters identify like partsthroughout.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a is a perspective view of a tubular housing of a spacer memberof the present invention.

FIG. 1 b is a cross-sectional view of a housing of the spacer member ofthe present invention filled with a ceramic material.

FIG. 2 is a graph showing the average cold crushing strength for variouspreferred castable ceramic core materials.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

As shown in FIGS. 1 a and 1 b, the spacer member of the presentinvention includes a housing 20 with core 30 of a ceramic material. Thehousing 20 is preferably in the form of a tube having a wall portionwith at least two substantially flat surfaces 40 in parallel with eachother and a bore 90 defined by the wall portion that is structured toreceive the ceramic core. As shown in FIG. 1 a, housing 20 can have anyfunctional dimensions, however, typical spacer members have a width (W)of from about 1 to about 4 inches, a height (H) of from about 2 to 6inches, and a length (L) of from about 6 to 24 inches.

The thickness of the flat surfaces 40 of the housing 20 can be fromabout 1/64 inch to about ½ inch, preferably from about 1/16 inch toabout ⅛ inch. While thicker walls can be employed, relatively thin wallsare typically desirable due to the considerable weight savings. Thinnerwalls allow for a lower weight for the spacer member, however, if thewalls are too thin (e.g., less than about 1/64 inch), the spacer membermay be prone to crushing and tearing under the ingot load.

The exterior of the flat surfaces 40 of the housing 20 are preferablysmooth to minimize any mechanical interlocking with ingot surface duringa heat treatment. A suitable maximum roughness is an Ra of about 10 toabout 10,000 microinches. The smoothness of the flat surface exterior 40may be controlled by the extrusion process or rolling process used tomanufacture the housing 20. In one embodiment of the present invention,the surfaces 40 may be machined or polished as needed.

The exterior of the flat surfaces 40 of the housing 20 also may becoated with a material to further prevent ingot sticking in the preheatfurnace. The preferred material used is the metal oxide coating nickelaluminide, but other metal oxide coatings such as nickel oxide, nickelaluminide, cobalt oxide, chromium oxide, molybdenum oxide, zirconiumoxide, aluminum oxide, and magnesium oxide could also be used.

In one embodiment of the present invention, the thermal oxide of nickelformed on the exterior of the flat surfaces 40 of the housing 20 has athickness of from about 5 nm to about 50 microns. In another embodiment,the thermal oxide of nickel formed on the exterior of the flat surfaces40 has a thickness of from about 10 nm to about 2 microns.

While the exterior of only two opposing flat surfaces 40 need to besmoothed and/or coated as described above when used to support ingots ina preheat furnace, it is preferred that the exterior of all of the flatsurfaces 40 are similarly treated. In this manner, a user need not beconcerned which of the exterior surfaces 40 contact an ingot in apreheat furnace.

The flat surfaces 40 have corner edges 50 that have an outside radius ofcurvature R₀ of at least ⅜ inch and ends 80 that are tapered at least ¼inch inward toward a bore 90 defined by the wall portion that isstructured to receive the ceramic core. This reduces high stress risersthat contribute to premature failure at the corner edges 50 and reducesthe potential for sticking of the ingot to the spacer member. Therounded corner edges 50 may be any suitable shape having some degree ofcurvature, such as circular, elliptical, or ovular. In the preferredembodiment, the rounded corner edge 50 extends longitudinally along thelength of the spacer member. By rounding the interior of the corneredges 50, the load of the ingots applied to the housing 20 is partiallyshifted away from the edges 50 to reduce stress at the edges 50.Furthermore, when spacer blocks have pointed or sharply angled corneredges 50, sharp divots or deep deformations can form in the ingot at thepoint of contact between the spacer block corner edge 50 and the softingot. The sharper and/or deeper the resulting ingot deformation is, themore remedial processing is required to remove the defect from the ingotfor subsequent use. Additional remedial processing contributes greatlyto the expense of the resulting product. Accordingly, by rounding thecorner edges 50 of the spacer members, the subsequent remedial ingotprocessing is reduced and the lifespan of the spacer member isprolonged.

The tubular housing 20 comprises a metal selected from the groupconsisting of high temperature steel, high temperature steel alloy, orcold rolled steel. High temperature steel or steel alloys are preferredbecause the solidus temperature of steel is significantly higher thanthe temperature of the preheat furnace conditions. Steel and steelalloys also exhibit tensile compressive yield strengths that aresufficient to support the weight of ingot loads at the preheat furnacetemperatures. Preferred high temperature steel or steel alloys are 1018and 1020. High temperature steel and steel alloys are particularly wellsuited for use in relatively high temperature furnaces employingtemperatures of from about 800° F. to about 1,200° F. (427° C.-649° C.).

In one embodiment, the spacer member has a thickness of from about 0.5to about 4 inches. Spacer members less than about 0.5 inch thick do nottypically allow for adequate circulation of the furnace atmospherebetween ingots, and spacer members sized larger than about 4 inchesthick result in an ingot stack that is too tall for conventional preheatfurnaces and may destabilize the ingot stack. In one embodiment of thepresent invention, housing 20 has a square cross-sectional configurationand dimensions of about 3 inch×3 inch×12 inch. In another embodiment,the housing 20 has a rectangular cross-sectional configuration anddimensions of about 2 inches×5 inches×16 inches. Each of these preferredembodiments are sized and configured to conform with the conventionalspacer blocks presently used in the ingot processing industry, however,other cross-sectional configurations of the housing 20 are encompassedby the present invention.

Housing 20 is designed to enclose at least a part of the ceramic core30. The core 30 is preferably manufactured from a curable ceramicmaterial. Ceramic materials typically have a relatively low density(compared to aluminum) and high strength. However, most ceramicmaterials are brittle and tend to crumble under impact loads, thereforespacer member includes housing 20 to retain the ceramic core 30. Thehousing 20 also serves to prevent the ceramic material from contactingand damaging ingots during use. Accordingly, the ends 80 of the housing20 should be substantially closed off to prevent escape of the ceramiccore 30 during use as shown in FIGS. 1 a and 1 b.

The ceramic core 30 may comprise a castable material, such as calciumaluminates. The ceramic material preferably has a cold crushing strengthof from about 500 psi to about 20,000 psi. Cold crushing strength is ameasure of the static load the spacer member can withstand until failureoccurs. The density of the ceramic material preferably is less than thedensity of conventional solid aluminum spacer blocks (about 173 lbs/ft³or 2.8 g/cc) to achieve significant weight savings for the spacer memberof the present invention. Typically, the density of the ceramic materialis not greater than about 150 lbs/ft³ or 2.4 g/cc. Preferably, thedensity of the ceramic material is not greater than about 125 lbs/ft³ or2.0 g/cc. The properties of the ceramic material of cold crushingstrength and density are balanced to obtain a suitable material for thecore 30.

Particularly preferred castable materials include Greenlite Express 24,CW108 Castable, HPV Castable, Reno Cast FSLC/A1, and Metroflo SR. Thesepreferred castable materials are available from RHI Refractories(Greenlite & CW108), Chicago Fire Brick Division (HPV), Renofractories,Inc. (Reno Cast), and Matrix Refractories, Inc. (Metroflo). Theseceramic materials were evaluated for suitability for use in the core 30of the spacer member of the present invention. FIG. 2 illustrates theaverage cold crushing strength of each of these preferred castablematerials. From the figure, Reno Cast FSLC/A1 and Metroflo SR have thegreatest cold crushing strength and therefore would be the mostpreferred castable material.

At least one end portion 60 of the housing 20 comprises at least oneaperture 70 having a diameter of from about 1/64 inch to about 1/16 inchsized to allow the inside of the spacer member to adjust to the ambientatmospheric pressure of the furnace while substantially retaining theceramic core 30. In another embodiment, a plurality of end portions 60of housing 20 contains a plurality of apertures 70. The end portions 60are attached to the ends 80 of the housing 20.

The method of making a spacer member includes: providing a tubularhousing 20 comprising a wall portion having at least two substantiallyflat surfaces 40 in parallel with each other and a bore 90 wherein theflat surfaces 40 have corner edges 50 and ends 80; tapering the ends 80at least ¼ inch inward toward the bore 90 of the tubular housing 20;attaching an end portion 60 having at least one aperture 70 to an end 80of the tubular housing 20; filling the tubular housing 20 with a ceramicmaterial; attaching an end portion 60 having at least one aperture 70 tothe other end 80 of the tubular housing 20; and applying to the flatsurfaces 40 of the wall portion a non-stick coating for preventingsticking of a heat treated metallic alloy product to the spacer member.

The housing 20 may be formed by extruding the steel into a tube of thedesired shape or by providing a sheet of steel, shaping the sheet ofsteel into the desired configuration, and welding the edges of the sheettogether to form a tube. In a preferred embodiment of the presentinvention, a low cost housing 20 is made from cold rolled steel androbotically welded. In another embodiment, the housing 20 is roll formwelded in the same flow path.

After the housing 20 is formed, one end of the housing 20 may be closedoff by attaching an end portion 60 comprising at least one aperture 70having a diameter of from about 1/64 inch to about 1/16 inch sized toallow the inside of the spacer member to adjust to the ambientatmospheric pressure of the furnace while substantially retaining theceramic core 30. After an end 80 of the housing 20 is closed off, theuncured ceramic material is then poured into the housing 20 and allowedto cure. The other end 80 of the housing 20 may then be closed off. Inthis manner, the housing 20 acts as a shell surrounding the ceramic core30.

In a preferred embodiment, tapering would occur by first cutting theends 80 along the corner edges 50 and then tapering the ends 80 inwardtoward the bore 90 of the tubular housing 20 via the use of a taperingmeans. However, one skilled in the art would know that tapering the endscould occur via the use of other methods. The length of the cut alongthe corner edges 50 can be from ¼ inch to 1 inch. A preferable means forcutting the corner edges 50 is milling, but could include sawing,shearing, or grinding. Tapering means includes anything that would bestrong enough to bend the metal including a break or a radius formingjig. An end portion 60 is then attached to the housing 20 preferably bywelding the end portion 60 to the ends 80 of the housing 20. However,the end portion 60 could also be attached via the use of fasteners orany means that would properly attached the end portion 60 to the ends 80of the housing 20.

A coating comprising a thermal oxide of nickel, specifically nickelaluminide, is then formed on the exterior of the flat surfaces 40 of thehousing 20. Nickel or nickel alloys can be applied to the flat surfaces40 of the housing 20 prior to forming the housing 20 or after thehousing 20 is manufactured via conventional coating techniques, such asbrushing, plasma spraying, thermal spraying, cold spraying,electroplating, electroless plating, cladding, plasma vapor deposition,sputtering, and electron beam evaporation.

After applying a nickel aluminide coating to the flat surfaces 40 of thewall portion, the housing 20 is preferably subjected to an oxidizingstep. The oxidizing step comprises subjecting the housing 20 to aheating period in an oxidizing atmosphere, in which the housing 20 isheld to an elevated temperature of from about 800° F. to about 1200° F.(427°-649° C.) for greater than 2 hours. The high temperature heatingstep is beneficial in forming a thick non-reactive oxide on the surfaceof the coating and to form a diffusion layer between the coating and thehousing 20. In another embodiment of the present invention, housing 20can be subjected to a standard plasma spray process. In yet anotherembodiment of the present invention, housing 20 can be subjected toozone or another oxidizing atmosphere for a period of time sufficient toallow a nickel oxide to form on housing 20.

It will be readily appreciated by those skilled in the art thatmodifications may be made to the invention without departing from theconcepts disclosed in the forgoing description. Such modifications areto be considered as included within the following claims unless theclaims, by their language, expressly state otherwise. Accordingly, theparticular embodiments described in detail herein are illustrative onlyand are not limiting to the scope of the invention which is to be giventhe full breadth of the appended claims and any and all equivalentsthereof.

1. A spacer member for supporting a metallic alloy product during heattreatment, said spacer member comprising: a ceramic core; and a tubularhousing comprising a wall portion, a bore defined by said wall portionthat is structured to receive said ceramic core, and two end portions,said housing enclosing said ceramic core, said housing wall portionhaving at least two substantially flat surfaces in parallel with eachother, said flat surfaces having corner edges having a radius of atleast ⅜ inch and ends being tapered at least ¼ inch inward toward saidbore of said tubular housing, said end portions each having at least oneaperture.
 2. A spacer member of claim 1 wherein said flat surfaces havea non-stick coating comprising a thermal oxide of nickel.
 3. A spacermember of claim 2 wherein said non-stick coating consists of nickelaluminide.
 4. A spacer member of claim 2 wherein said non-stick coatinghas a thickness of from about 5 nm to about 50 microns.
 5. A spacermember as in claim 1 wherein said tubular housing comprises a metalselected from the group consisting of a high temperature steel, a hightemperature steel alloy, or a cold rolled steel.
 6. A spacer member asin claim 1 wherein said aperture of said end portion is from about 1/64inch to about 1/16 inch in diameter.
 7. A spacer member for supporting ametallic alloy product during heat treatment, said spacer membercomprising: a ceramic core; and a tubular housing comprising a wallportion, a bore defined by said wall portion that is structured toreceive said ceramic core, and two end portions, said housing enclosingsaid ceramic core, said housing wall portion having at least twosubstantially flat surfaces in parallel with each other, said flatsurfaces having corner edges having a radius of at least ⅜ inch and endsbeing tapered at least ¼ inch inward toward said bore of said tubularhousing, said end portions each having at least one aperture, said flatsurfaces having a non-stick coating comprising a thermal oxide ofnickel.
 8. A spacer member of claim 7 wherein said non-stick coatingconsists of nickel aluminide.
 9. A spacer member of claim 7 wherein saidnon-stick coating has a thickness of from about 5 nm to about 50microns.
 10. A spacer member as in claim 7 wherein said tubular housingcomprises a metal selected from the group consisting of a hightemperature steel, a high temperature steel alloy, or a cold rolledsteel.
 11. A spacer member as in claim 7 wherein said aperture of saidend portion is from about 1/64 inch to about 1/16 inch in diameter. 12.A method of making a spacer member for supporting a metallic alloyproduct during heat treatment, said method comprising the steps of:providing a tubular housing comprising a bore and a wall portion havingat least two substantially flat surfaces in parallel with each other,said flat surfaces having corner edges and ends; tapering said ends atleast ¼ inch inward toward said bore of said tubular housing; attachingan end portion comprising at least one aperture to one of said ends ofsaid flat surfaces; filling the tubular housing with a ceramic material;attaching another of said end portions comprising at least one apertureto another of said ends of said flat surfaces; and applying to said flatsurfaces of said wall portion a non-stick coating for preventingsticking of a heat treated metallic alloy product to said spacer member.13. The method of claim 12 further comprising subjecting said tubularhousing to a high temperature heating step after applying said non-stickcoating wherein said tubular housing is held at an elevated temperatureof from about 800 degrees F. to about 1200 degrees F. (427°-649° C.).14. The method of claim 12 wherein tapering said ends comprises cuttingsaid ends along said corner edges and tapering said ends via the use ofa tapering means.
 15. The method of claim 14 wherein said tapering meanscomprises a break or radius forming jig.
 16. The method of claim 12wherein said tubular housing comprises a metal selected from the groupconsisting of a high temperature steel or steel alloy or cold rolledsteel.
 17. The method of claim 12 wherein said non-stick coatingcomprises a thermal oxide of nickel.
 18. The method of claim 12 whereinsaid non-stick coating consists of nickel aluminide.
 19. The method ofclaim 12 wherein said non-stick coating has a thickness of from about 5nm to about 50 microns.
 20. The method of claim 12 wherein said apertureof said end portion is from about 1/64 inch to about 1/16 inch indiameter.
 21. The method of claim 12 wherein said flat surfaces havecorner edges having a radius of at least ⅜ inch.
 22. A method of makinga spacer member for supporting a metallic alloy product during heattreatment, said method comprising the steps of: providing a tubularhousing comprising a bore and a wall portion having at least twosubstantially flat surfaces in parallel with each other, said flatsurfaces having corner edges and ends; tapering said ends at least ¼inch inward toward said bore of said tubular housing, wherein said endsare cut along said corner edges and tapered via the use of a taperingmeans; attaching an end portion having at least one aperture to one ofsaid ends of said flat surfaces; filling the tubular housing with aceramic material; attaching another of said end portions comprising atleast one aperture to another of said ends of said flat surfaces; andapplying to said flat surfaces of said wall portion of said tubularhousing a non-stick coating for preventing sticking of a heat treatedmetallic alloy product to said spacer member, wherein said tubularhousing is held at an elevated temperature of from about 800 degrees F.to about 1200 degrees F. (427° C.-649° C.) after applying said non-stickcoating.
 23. The method of claim 22 wherein said tapering meanscomprises a break or radius forming jig.
 24. The method of claim 22wherein said tubular housing comprises a metal selected from the groupconsisting of a high temperature steel or steel alloy or cold rolledsteel.
 25. The method of claim 22 wherein said non-stick coatingcomprises a thermal oxide of nickel.
 26. The method of claim 22 whereinsaid non-stick coating consists of nickel aluminide.
 27. The method ofclaim 22 wherein said non-stick coating has a thickness of from about 5nm to about 50 microns.
 28. The method of claim 22 wherein said apertureof said end portion is from about 1/64 inch to about 1/16 inch indiameter.
 29. The method of claim 22 wherein said flat surfaces havecorner edges having a radius of at least ⅜ inch.